The invention relates to methods and apparatus for coupling explosive devices in tools for use in well bores.
After a well has been drilled and casing has been cemented in the well, one or more sections of the casing may be perforated using perforating guns. After a perforating gun string is lowered into the well to a desired depth, the guns in the string arc fired to create openings in the casing and to extend perforations into the surrounding formation. Production fluids in the perforated formation can then flow through the perforations and the casing openings into the well bore.
A gun string may include one or more carriers each housing a number of shaped charges coupled to a detonating cord. To fire the shaped charges, the detonating cord is initiated, with the detonation wave traveling through the cord detonating successive shaped charges connected to the cord. A connector sub or adapter couples one gun carrier to the next. To transfer a detonation wave carried by the detonating cord in one gun carrier to the detonating cord of a successive gun carrier, the connector sub or adapter conventionally includes booster explosives that are coupled to the detonating cords. In one arrangement, the detonation wave transmitted down a detonating cord in a first gun carrier is transferred to a donor booster explosive in the adapter. In turn, the donor booster explosive initiates a detonation wave in a receptor booster explosive, which transfers the detonation wave to the detonating cord of the next gun carrier.
Due to tensile forces imposed on the detonating cord resulting from such forces as mechanical loading, tool vibration, and thermal expansion or shrinkage, physical separation of the detonating cords from their respective booster explosives may occur. This reduces the reliability of the transfer of a detonation wave between a booster explosive and a detonating cord in conventional connector subs or adapters.
In addition, detonation of a booster explosive may cause damage to an adapter. A typical adapter may include O-ring seals, threaded connectors, and other elements that when damaged prevent reuse of the adapter. This increases the cost of well operations since damaged adapters must be replaced, sometimes after only a small number of uses.
A need thus exists for an improved coupling method and apparatus for explosive devices in tools, such as perforating gun strings, for use in well bores.
In general, according to one embodiment, a gun system includes a first carrier including a detonating cord and a second carrier including a detonating cord. An adapter couples the first and second carriers, with the adapter including an explosive coupled to the detonating cord of one of the first and second carriers. The explosive is positioned in a reduced housing portion of the adapter. The reduced housing portion of the adapter has a first outer diameter less than an inner diameter of the first carrier to provide a predetermined annular space between the reduced adapter portion and the inner diameter of the first carrier.
In general, according to another embodiment, a tool includes a detonating cord, an explosive coupled to the detonating cord, and a retainer element spaced apart from the explosive and attached to the detonating cord. The retainer element is positioned in the tool to reduce longitudinal movement of the detonating cord away from the explosive.
In general, according to yet another embodiment, an adapter for coupling to a tool includes one or more housing sections and at least one of a scaling element and a connector element contained in the one or more housing sections. Further, an explosive is positioned a predetermined axial distance in the one or more housing sections away from the at least one of a sealing element and a connector element to protect the elements from detonation of the explosive.
Other features and embodiments will become apparent from the following description, the drawings, and the claims.